Conditions have now been deterined for producing suspensions of heparin particles having a high fraction with diameter less than one micron. Films and coatings of poly(lactic acid) containing such particles will now be produced in which the heparin concentration is varied and the method of removal of solvent from the coatings is also varied. The effect of these variables of the release rate of the heparn will be studied. Vascular graft materials will be coated with these heparin-releasing polymers and a sequence of in vivo tests begun to assess tissue reaction in rabbits and rats, and thrombus formation characteristics after implantation in dogs. Studies will be continued of the effect of differing concentrations of promising platelet-inhibiting agents, including prostocylin, being released from poly(lactic acid). Platelet adhsion will be studied using the centrifugal method of assessing adhesive strength. In vivo tests will also be conducted with coatings releasing these agents, alone and in combination with heparin release.